The present invention relates to a plasma display panel and image display apparatus using the same, which are used as an information processing terminal, for a flat-type or wall-hanging type television, or the like.
The gas discharge type display such as plasma display makes displaying by self-light emission, and thus it has wide field-of-view angle and provides a better easy-to-watch displaying characteristic. In addition, it can be produced to be thin and large-sized. The application of the plasma display has begun to the displays for information terminal equipment and high-definition television receivers. The plasma display can be roughly classified into DC drive type and AC drive type. Of these types, the AC drive type plasma display has developed to the extent that the brightness can be increased by the memory action of the dielectric layer covering the electrodes, and that its life span can be extended enough to bear practical use by forming a protective layer. The result is that the plasma display is now being put to practical use as a multi-purpose video monitor.
The AC drive type plasma display is generally composed of a front plate, a back plate, and a discharge space region that is formed between the front and back plates and that has a great number of cells partitioned by walls. The front plate has formed therein a plurality of pairs of display electrodes. The back plate has formed therein a plurality of address electrodes that are substantially perpendicular to these display electrodes. When a pulse voltage is applied between the address electrodes and display electrodes, an auxiliary discharge is caused in the respective cells formed by the front and back plates and the partition walls. Under this auxiliary discharge, a main discharge is caused by applying a pulse voltage between the display electrodes of the respective pairs of the front plate formed to oppose the respective cells. The ultraviolet light from the main discharge excites the phosphor to emit light. The light from the phosphor is passed through the front plate, thus displaying and light emission being made.
This conventional AC drive type plasma display made displaying and light emission by surface discharge between the display electrodes of each pair. An example of this conventional AC drive type plasma display is described in JP-A-5-190099.
A first object of the invention is to provide exactly a novel AC type plasma display panel with the light emission efficiency improved.
A second object of the invention is to provide an AC type plasma display panel with the discharge efficiency improved by producing positive columns.
A third object of the invention is to improve the discharge efficiency in the plasma display panel.
In order to achieve the first object in accordance with the invention, there is provided a plasma display panel having at least a back plate that has a plurality of address electrodes and a plurality of first display electrodes arranged to intersect with the address electrodes, and a front plate that has a plurality of second display electrodes arranged to oppose the plurality of first display electrodes so that discharge can be caused between the second electrode and the first display electrode addressed by use of the address electrodes.
Since the first and second display electrodes are opposed to each other, or employ an opposite electrode structure, the gap length between the first and second display electrodes can be made substantially constant in the display electrode plane. In addition, since the display electrodes of each pair can be respectively formed on the front and back plates for each electrode area to be wide, a stable discharge phenomenon can be caused. In other words, even if wall charge is generated between both the display electrodes, the discharge current can be kept stable (current density maintained constant) since the gap length in the display electrode plane is constant. Moreover, since the electrode area can be made large, the light emission duty can be increased, and thus the light emission efficiency is large enough.
In addition, since the display electrodes employ the opposite electrode structure, the wiring resistance of the second display electrodes formed by transparent electrodes and opaque electrodes (bus electrode) can be easily decreased since each electrode width can be increased in a plane as described above. Similarly, since only the first display electrodes are formed on the back plate, the electrode width can be made wider than those in the surface discharge type, and thus the wiring resistance of the electrodes can be much decreased. Thus, since the wiring resistance can be remarkably reduced, low consumption power can be achieved, leading to high light emission efficiency. Also, since the voltage drop on the driven display electrodes can be remarkably reduced, the operation margin can be increased.
In addition, since the display electrodes employ the opposite electrode structure, partition walls of high aspect ratio can be used, and the partition wall area on which phosphor is coated can be increased to raise the visible light taking out efficiency. In other words, the light emission efficiency of the panel can be improved.
Moreover, in the above structure, if a plurality of first display electrodes are respectively inherent electrodes (Y electrodes), and if a plurality of second display electrodes are a common electrode (X electrode) to those electrodes, the second display electrode can be formed by a single plane electrode to cover the entire surface of the panel. By use of the single plane electrode to cover all panel, it is possible not only to decrease the resistance of the second display electrodes but also to remove the highly precise etching process used so far for making transparent electrodes of a display electrode pattern.
Forming the second display electrodes in a single plane shape makes electric charge to easily move to other display cells, but the partition walls formed in a lattice shape to surround the display cells can suppress the charge movement, and thus prevent erroneous discharge in the other display cells.
Moreover, if the second display electrodes are formed by a transparent plane electrode and a bus electrode deposited thereon, and if the bus electrode is formed in a lattice shape to overlap the lattice-shaped partition walls, the resistance of the second display electrodes can be decreased without decreasing the opening rate as compared with the structure having the line-shaped bus electrode. In other words, if the opaque bus electrode as bus electrode is formed to match the shape of the partition walls of the display cells, the opening rate of the display cells can be remarkably increased to improve the brightness since it does not depend on the shape and size of the opaque electrode.
In addition, if the transparent electrode pattern of the second display electrodes is formed similar to the line-shaped electrode pattern of the first display electrode (opaque electrode), the stability of the repetitive discharge characteristic can be much improved against the generation of the wall charge. Both the display electrodes at this time are arranged parallel or perpendicular to each other. Since the bus electrode formed on the transparent electrode is formed to overlap on the lattice-shaped partition walls, the resistance of the display electrodes can be reduced, the opening rate of the display cells can be improved, and the capacitance between the electrodes can be decreased (openings are made up by forming a line pattern, reducing the electrode area). Particularly, since the effect of the bus electrode shape is little, this feature is advantageous to the highly minute structure of the panel.
In order to achieve the second object in accordance with the invention, there is provided a plasma display panel having at least a back plate that has a plurality of address electrodes and a plurality of first display electrodes arranged to intersect with the address electrodes, and a front plate that has a plurality of second display electrodes arranged to oppose the plurality of first display electrodes so that discharge with a positive column formed is caused between the second display electrode and the first display electrode addressed by use of the address electrodes.
Thus, since the display electrodes employ the opposite electrode structure, the distance between the first and second display electrodes necessary to make the positive column can be assured even if the size of the discharging cells is limited because of the highly minute structure of the panel. Therefore, since the positive column is generated by the above structure, the discharge efficiency can be increased as compared with the negative glow. The discharge efficiency is the amount of ultraviolet light generated per unit electric power. The ultraviolet light rays excite the phosphor to emit visible light. Here, the term, positive column, is one of the light emission states in the normal glow mode of glow discharge. In other words, although cathode dark space, negative glow, Faraday dark space, and positive column are caused in this order in the direction from the cathode to anode, display light emission operation is performed by chiefly using the positive column to radiate ultraviolet rays. This is because the discharge efficiency of the positive column is higher than the negative glow. In this case, a constant-intensity field is produced in the axis direction of the positive column. Since this field strength is determined by the energy which the electrons gain per unit length in the wall surface direction of the display discharge cells, and the energy lost by elastic collision or the like, if the diffusion to partition walls is suppressed as a fluorescent light, the discharge light emission characteristic of the positive column depends on the length of the discharge cells in the wall surface direction, but does not depend on the gap length between the opposite electrodes. Therefore, if even the gap length enough to stabilize the positive column can be assured, more increasing the gap length will not cause a larger field strength on the neighborhood of the partition walls, and the discharge maintaining current (discharge current density) for maintaining normal glow discharge can be fully reduced.
However, when the cell size or tube diameter of the panel becomes small enough, the energy loss due to the diffusion to partition walls cannot be neglected. In order to solve such difficulty, a constant bias voltage is applied to the metal partition walls that are arranged between the front and back plates and have the surface insulated. Thus, the electric field intensity (potential difference) in the wall surface direction which is necessary for the formed positive column can be stably and efficiently maintained through the ion sheath formed near the surface of the insulating (dielectric) layer, thereby generating the positive column to much improve the discharge efficiency.
The discharge maintaining current has been increased so far in order to make the positive column stable, thus the current density exceeding a constant level. Therefore, ultraviolet light is saturated except for the stability of discharge, thus limiting the improvement of discharge efficiency to some extent. If a bias voltage is applied to the metal partition walls to produce a wall voltage (wall charge) on the dielectric layer of the metal surface, the charged particles are suppressed from being neutralized, and the excessive energy loss due to the diffusion to partition walls is decreased. Thus, the discharge can be maintained stable even by decreasing the discharge maintaining current (current density). Therefore, the amount of charge necessary for maintaining the discharge (the minimum current necessary for maintaining the discharge) can be assured without saturating the ultraviolet light, and the discharge efficiency can be improved.
In addition, the metal sheets with the surfaces insulated are laminated to form a plate for this metal partition walls. If a bias voltage is applied to at least one of the metal sheets, the metal sheets each covered with an insulating (dielectric) layer are self-biased therebetween so that an electric field intensity (potential difference) can be generated in the axial direction. Consequently, the electric field intensity (potential difference) necessary for the formed positive column can be generated effectively and stably as compared with the single metal plate. Since the stable positive column can be produced in this way, the discharge maintaining current density for the normal glow discharge can be fully reduced. Thus, the positive column can be produced under the condition that the ultraviolet light rays are not saturated, and the discharge efficiency can be maximized.
Although the opposite electrode structure described so far has difficulty in the driving operation, increasing the gap length between the opposite X, Y display electrodes will increase the firing potential Vo which depends on the gap length, and the field crosstalk and charge crosstalk which affect the adjacent cells, use of metal partition walls with the sides covered with an insulating material and making the potential appropriate by applying a bias voltage as described above can reduce the gap length between the X, Y display electrodes effectively (increase the field strength between the electrodes), and the shield between the adjacent cells can prevent the field from being leaked and the associated unnecessary charge from being generated.
More specifically, since the effective gap length between the first and second display electrodes can be reduced by this metal partition wall, the firing potential Vo, or the operating point voltage at the first discharge light emission time can be reduced.
A load straight line (load resistance, current limiting resistance) is used to control the discharge maintaining current at the operating point and make the discharge efficiency appropriate. This operating point is given by the intersection between the load straight line and the current voltage characteristic curve (I-V characteristic curve) of the cells themselves. Since the I-V characteristic of the cells themselves suppresses the diffusion to partition walls according to the invention, the low current region (normal glow discharge region) is expanded. Therefore, the current at the operating point which is set by the load straight line can be reduced more stably by about one place or above than by means.
Since the wall voltage is generated on the display electrode in the cell structure of AC drive type, it affects the normal glow voltage Vn. This normal glow voltage Vn is chiefly given by the cathode drop voltage Vc or the potential of positive column in the axial direction (the product of the electric field strength E in the axial direction and the length l substantially equal to the gap between the electrodes). When the positive column is produced by AC type drive, the wall voltage can be used at the discharge start time as compared with the DC type drive, and thus the normal glow voltage Vn, or the cathode drop voltage Vc can be apparently reduced. Therefore, the AC type drive is able to apparently decrease the operating point voltage (normal glow voltage Vn) by the value corresponding to the wall voltage with respect to the I-V characteristic of the cell themselves since the wall voltage is generated.
Thus, the normal glow discharge region of the I-V characteristic is made to meet low current and low voltage by suppressing the diffusion to partition walls of the positive column under the AC type drive. Accordingly, while stable discharge (positive column) is being maintained (generated), the operating point current and voltage according to the load straight line can be reduced at a time. Since the current and voltage at the operating point are low, the consumption power can be reduced, and also the discharge maintaining current (current density) can be made appropriate. Thus, the discharge efficiency can be remarkably improved.
In the plasma display panel having a great number of display cells formed by the front and back plates that have electrodes connected to a drive circuit system, and the partition walls held between those plates, the partition walls are formed by a single metal sheet with the surface insulated or by laminating a plurality of metal sheets with the surfaces insulated. At least one of the sheets of the partition walls is connected to the drive circuit system in order to be biased by a bias voltage. The electrodes and the partition walls having at least one of the sheets to which a bias voltage is applied are respectively connected to proper load resistances.
Thus, address discharge is caused between the A, Y electrodes within a selected display cell so that wall charge is generated on the Y electrode. Preliminary discharge is caused between the Y electrode with wall charge generated and the metal walls supplied with a bias voltage and serving as electrodes so as to produce priming particles. The generated priming particles can reduce the firing potential Voxxe2x88x92y between the X, Y display electrodes. The discharge can be stably maintained under the discharge maintaining voltage that is reduced by the amount corresponding to the wall voltage.
Moreover, this metal partition wall structure is able to solve the light penetration phenomenon (light crosstalk) appearing in the display cells surrounded by dielectric partition walls.
Therefore, this opposite electrode structure is constructed by use of the metal partition walls considering process and assembly, firing potential, and various types of crosstalk.
In addition, when the metal partition walls are used, the capacitance between the opposite X, Y display electrodes is increased, and thus the consumption power is increased in proportion to the CV2 per pulse. However, if the metal partition walls are made in contact with or connected to the front plate or back plate through a plurality of projections formed on the metal partition wall side or front or back plate side, that increase can be suppressed.
More specifically, in the plasma display panel having a plurality of display cells formed by the front and back plates that have electrodes connected to a drive circuit system, and the partition walls held therebetween, a plurality of projections are provided on the surfaces of the partition walls opposed to the front or back plate and arranged not to be made in contact with the electrodes formed on the front or back plate, thereby making it possible to suppress the capacitance from increasing due to the metal partition walls. In addition, when a single plane electrode is formed on the front plate as a common display electrode to the plurality of display cells, openings should be locally provided in the plane electrode so that the projections on the partition walls cannot be made in contact with the plane electrode. Thus, the contact area or connection area between the metal partition walls and the front or back plate can be reduced, resulting in the decrease of the capacitance between the X, Y electrodes. In this case, it is preferable that the projections be arranged not to overlap on the electrodes formed on the front or back plate. Moreover, since the electrode surface is required to have an insulating layer improved in its dielectric strength, it is preferable that when the metal partition walls are formed by laminating a plurality of metal sheets with the surfaces insulated, all the metal sheets not be used as (driving) electrodes to which a bias voltage is applied. Even if the metal partition walls are applied to the conventional surface discharge type plasma display panel, the capacitance between the address electrodes and display electrodes arranged to oppose can be suppressed from increasing.
Also, in the cross structure of address electrodes and display electrodes Y mentioned so far, if the firing potential Voaxe2x88x92y is tried to decrease by reducing the thickness of the insulating layer between the address electrode A and display electrode Y, the dielectric strength of the insulating layer is reduced, degrading the reliability of the panel or the consumption power is increased with the increase of the interelectrode capacitance in proportion to the CV2 per pulse. On the other hand, in the display cell structure in which the front plate has on an insulating substrate a first insulating layer, A electrodes, a second insulating layer, Y electrodes, and a third insulating layer formed in this order, a fourth insulating layer of a single layer or multilayer structure (that prevents defects such as pinholes from being caused) for the electrodes Y is deposited between the second insulating layer and the Y electrodes.
Moreover, in the cross structure of the address electrodes A and display electrodes Y, if the capacitance between the electrodes and the dielectric strength of the insulating layer are respectively tried to decrease and increase by contrarily increasing the thickness of the insulating layer between the address electrodes A and display electrodes Y, the firing potential Voaxe2x88x92y is increased, and the drive IC is required to have high dielectric strength. In the display cell structure in which the back plate has, on an insulating substrate, a first insulating layer, A electrodes, a second insulating layer, Y electrodes, and a third insulating layer formed in this order, the third insulating layer covers the Y electrodes and their surrounding area, but does not cover at least part of the second insulating layer.
The present invention is based on the fundamental principle of operation found so far through our research to achieve the third object.
The principle uses the means for effectively and simultaneously establishing the high field region in the cathode dark space and the equipotential region in the positive column considering the glow discharge maintaining conditions as will be described below.
Metal partition walls with surfaces insulated and of high aspect ratio are arranged between the opposite display electrodes. A voltage substantially equal to that at the anode electrode is applied to the metal partition walls, causing a wall voltage Vw (wall charge Qw=Cxc2x7Vw0, where C is the capacitance of the dielectric on the surface of the metal partition walls) on the dielectric layer on the surface of the metal partition walls. The wall charge used to generate the wall voltage Vw is always anode potential considering the fact that the equipotential region of the positive column is substantially equal to the anode potential since this charge is required not to consume or not to exchange during the repetitive discharge. In order to make the drive circuit for the metal partition walls unnecessary, and to provide ground within the panel structure to thereby drive stably, the anode electrode is grounded. The stable wall voltage Vw is generated by self-balance, and the diffusion of charged particles to the partition walls (energy loss) due to the reduction of the cell size (tube diameter) is much suppressed, resulting in effective production of plasma (positive column). In addition, since the wall voltage Vq is generated on the display electrodes by the AC type drive in addition to the suppression of the diffusion to partition walls, the I-V characteristic (normal glow discharge region) of the cell themselves is changed to low current, low voltage region, and the current and voltage at the operating point according to the load line can be remarkably reduced. Thus, the discharge can be maintained stable even under the minimum necessary current density where the saturation of ultraviolet light (saturation of brightness) is not caused.
When the diffusion to partition walls is not fully suppressed, the discharge cannot be stably maintained even if the positive column can be produced. Therefore, the discharge maintaining current is required to increase, and thus the energy loss is increased, limiting the improvement of discharge efficiency to some extent.
By use of the above principle, it is possible to make the discharge maintaining current appropriate, and stably maintain the discharge under the minimum necessary current density at which saturation of ultraviolet light (saturation of brightness) is not caused. Thus, the discharge efficiency can be improved by one order of magnitude, or one place or above.
Moreover, the invention can be applied to other electronic apparatus for generating the positive column by using glow discharge than the plasma display panel. At least, the discharge efficiency, or ultraviolet light generation efficiency can be improved.